Obama: Trump candidacy has 'rattled' world leaders

President Barack Obama said Thursday that world leaders are "rattled" by Donald Trump — and "for good reason."

During a press conference in Japan, Obama said the American presidential election is being "very" closely watched overseas. He told reporters that "it's fair to say" world leaders are "surprised" Trump is the presumptive Republican nominee.

"They are not sure how seriously to take some of this pronouncements but they're rattled by him — and for good reason, because a lot of the proposals that he's made display either ignorance of world affairs or a cavalier attitude," Obama added.

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He suggested Trump's controversial proposals were more about "getting tweets and headlines" than "actually thinking through" what's needed to keep America safe or the "world on an even keel."

Obama spoke to reporters in Japan, where he later Thursday will become the first sitting U.S. president to visit the Hiroshima Peace Park Memorial.

While he addressed the historic event in his opening remarks, questions quickly shifted to the U.S. election race.

Obama acknowledged the challenges of the long-running battle for the Democratic candidacy.

"During primaries people get grumpy with each other," Obama said.

He told reporters that he's sure the contenders wish the fight was over.

"It's a grind," he added.